Apparatus and a method of inspecting pieces of cloth

ABSTRACT

A method and an apparatus for automatic inspection of flatly positioned pieces of cloth with a view to detecting impurities or other irregularities in pieces of cloth. The pieces of cloth are transported past a camera ( 10 ) that is, in cooperation with a digital storage unit, configured for producing a digital image of each piece of cloth or portions of each piece of cloth; and wherein the apparatus comprises one or more light emitters ( 11 ) with a view to illuminating at least that part of a piece of cloth that is within the field of vision of the camera ( 10 ). Each piece of cloth is conveyed from a receiver conveyor ( 12 ) to a delivery conveyor ( 13 ), the field of vision of the camera ( 1 ) being configured to have at least an open area ( 14 ) between these two conveyors ( 12, 13 ), whereby the digital image is recorded during the passage of a piece of cloth from the receiver conveyor ( 12 ) to the delivery conveyor ( 13 ).

BACKGROUND OF THE INVENTION

The present invention relates to an apparatus for the automaticinspection of flatly positioned pieces of cloth with a view to detectingimpurities or other irregularities therein and a method therefor.

By such methods and apparatuses it was previously known to convey eachpiece of cloth on the top side of a conveyor past a camera that islocated above the conveyor and photographically records the piece ofcloth from above. In those cases where the piece of cloth has just lefta rotary ironer following preceding laundering, it is advantageous toinspect that side of the piece of cloth that had been facing the ironingside, since this is the most smooth side and hence the side on whichimpurities and irregularities will be most visible.

Such inspection from the ironing side has entailed that the pieces ofcloth were to be turned before the inspection was carried out, whichmakes demands for both extra space and extra equipment. There issimultaneously a requirement, in special cases, for being able toinspect both sides of a piece of cloth, which also makes requirementsfor each piece of cloth being turned.

It is the object of the invention to provide a method and an apparatusthat will, without need for additional space or equipment, enableinspection of the side of the pieces of cloth that has been facing theironing side of a rotary ironer, and which enable inspection of both theone and the other or both sides of pieces of cloth.

SUMMARY OF THE INVENTION

This is obtained by an apparatus for automatic inspection of flatlypositioned pieces of cloth with a view to detecting impurities or otherirregularities; wherein the apparatus comprises means for transportingthe pieces of cloth past a camera (10) that is, in cooperation with adigital storage unit, configured for producing a digital image of eachpiece of cloth or portions of each piece of cloth; and wherein theapparatus comprises one or more light emitters (11) with a view toilluminating at least that part of a piece of cloth that is within thefield of vision of the camera (10), characterized in that the conveyancemeans comprises a receiver conveyor (12) and a delivery conveyor (13),the field of vision of the camera (1) being configured for comprising atleast an open area (14) between these two conveyors (12, 13), wherebythe digital image is recorded during the passage of a piece of clothfrom the receiver conveyor (12) to the delivery conveyor (13).

A method is also provided for automatic inspection of flatly positionedpieces of cloth with a view to detecting impurities or otherirregularities; wherein the pieces of cloth are transported past acamera (10) that is, in cooperation with a digital storage unit,configured for producing a digital image of each piece of cloth orportions of each piece of cloth; and wherein the apparatus comprises oneor more light emitters (11) with a view to illuminating at least thatpart of a piece of cloth that is within the field of vision of thecamera (10), characterized in that each piece of cloth is transferredfrom a receiver conveyor (12) to a delivery conveyor (13), the field ofvision of the camera (10) being configured for comprising at least anopen area (14) between these two conveyors (12, 13), whereby the digitalimage is recorded during the passage of a piece of cloth from thereceiver conveyor (12) to the delivery conveyor (13).

By allowing the pieces of cloth to pass an open area between twoconveyors, it becomes possible to inspect the piece of cloth from eitherthe one or the other side in the open area between the conveyors. Thusit is possible to inspect a piece of cloth from the side that facestowards the ironing side after the piece of cloth has left a rotaryironer, even in case it is the side that faces towards the receiverconveyor due to the fact that the inspection takes place in an open areabetween the receiver conveyor and the delivery conveyor. Thus, therecording of the digital images that is a prerequisite for theinspection to take place from the side(s) that is/are most appropriatein the relevant situation.

It will be possible herein to configure the receiver conveyor at ahigher level than the delivery conveyor, whereby the passage from theone to the other conveyor is accomplished substantially vertically andsuch that the inspection is accomplished in accordance with asubstantially horizontal line of sight. However, this is associated withcertain difficulties during the passage of the end of the pieces ofcloth that will have a propensity to drop down onto the deliveryconveyor when an end portion of the piece of cloth reaches the end ofthe receiver conveyor.

It is therefore preferred that the delivery conveyor and the receiverconveyor are located essentially flush with each other, the inspectionbeing performed along a line of sight that is substantiallyperpendicular to the two preferably horizontally extending conveyors.

There is located between the camera and the area between the twoconveyors a transparent cover. Hereby a physical barrier is obtainedthat is able to separate the very sensitive electronics in the camerafrom the pieces of cloth. This is particularly important in laundrieswhere the pieces of cloth come from a rotary ironer and thus emit bothheat and moisture that may adversely influence the camera and the lightemitters. Conveniently the covering is configured as a glass board.

The receiver conveyor and the delivery conveyor being locatedessentially in extension of each other and configured for conveying thepiece of cloth slidingly across the transparent cover between them, itis obtained that the transparent cover is continuously cleaned ofdeposits, if any, in the form of fluff or other impurities.

Advantageously the transparent cover forms a window in a closedcontainer, in which the camera is located. Hereby it is possible tomonitor accurately the climate in which the camera is situated such thatconstant temperature and humidity can be maintained. Thereby optimal andconstant conditions of operation for the camera are ensured. The widthof the pieces of cloth that are to be photographed by the camera beingconsiderable, a mirror arrangement is conventionally used that providesan optical distance between the camera and the pieces of cloth that isclose to the maximal width, and by positioning these mirrors in theclosed container, the mirrors are safeguarded against deposits ofparticles and fluff that might otherwise adversely affect the quality ofthe images recorded.

Advantageously, the light emitters are arranged between the camera andthe transparent cover, due to the fact that the transparent coverthereby also protects the light emitters. The light emitters canconveniently be arranged in the closed container. Of course it is alsopossible to arrange one or more light emitters opposite the transparentcover, and in that case the camera will record an image that derives atleast partially from light transmitted through the pieces of cloth.

Advantageously a light emitter is configured as an elongate light guidearranged transversally to the two conveyors along the area located therebetween, and such that the light guide is supplied with light at one orboth ends, and wherein the light guide is configured for emitting lightalong the longitudinal axis of the light guide.

Light emitters of this type are known, but herein the particularadvantage is obtained that the strongly heat-emitting light source canbe arranged at a suitable distance from the camera and in a place whereit is easy to provide for a suitable cooling. In previously knownapparatuses for this type of inspection, fluorescent tubes, such as egneon tubes were used, but it has been found to be difficult to obtain anentirely uniform illumination over the width that is required in case oflaundry machines, and besides the replacement of burnt-out neon tubeshave required more protracted operation halts with ensuing adverseeffects on the production. Finally it is necessary to locate thefluorescent tubes quite close to the pieces of cloth, which has resultedin a heating of the pipes with ensuring variations in the lightemission. Further it should be noted that light guides are considerablyless space-consuming than fluorescent tubes, which makes it possible tokeep the open space between the two conveyors suitably narrow, wherebythe distance to be travelled by the piece of cloth without beingsupported by a conveyor is limited as much as possible.

A convenient configuration of the light guides is obtained in case theyeach comprise a glass rod that has, along its longitudinal axis,dispersion means for causing the light to leave the glass rod along thelongitudinal axis. A suitable dispersion means could in this case beconstituted of one or more ground facets distributed along thelongitudinal axis of the rod. The ground surface(s) of a facet willdisperse the light and thus the dispersed light will hit the surface ofthe glass rod at an angle that allows the light to leave the rod.Conveniently rods of quartz glass are used that are transparent to alight over a wide wavelength area.

Use of light guides of the above-mentioned type makes it particularlysimple to insert filters at the end of each rod between the rod and thelight source. Thus, the spectral composition of the light can beregulated in accordance with the type of laundry to be inspected.Replacement of burnt-out bulbs in the light source can be carried out ina readily accessible spot at a side portion outside the closedcontainer, and thus replacement of bulbs becomes possible withoutconsiderable operational disturbances.

It is preferred to use light with a mixture of wavelengths in theultraviolet range and the blue-violet range.

Now follows a detailed explanation of an exemplary, concrete embodimentof the invention with reference to the figures of the drawing, wherein

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a lateral view of a rollway, comprising a rotary ironer, aninspection apparatus according to the invention and a folding machine;and

FIG. 2 is an enlarged sectional view of FIG. 1 and shows the inspectionapparatus in combination with the receiver conveyor.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a common rotary ironer 1, to the outlet end of which thereis coupled a receiver conveyor 12. The pieces of cloth are conveyed fromthe receiver conveyor 12 onto a delivery conveyor 13 and from there thepieces of cloth are delivered to, e.g. a folding machine 2 that foldsthe pieces of cloth. Between the receiver conveyor 12 and the deliveryconveyor 13 there is an open space 14, where the pieces of cloth are notsupported by a conveyor. Underneath the open area there is located acamera 10 that is, via a number of mirrors S1, S2 and S3, configured forphotographing the area 14 between the two conveyors.

In the example shown in FIG. 1 the receiver and delivery conveyorsfollow each other at approximately the same level, but it is also anoption to configure the delivery conveyor 12 at a level below thereceiver conveyor 13, whereby the pieces of cloth will, during thetransfer between the conveyors, be freely suspended, and then toconfigure the camera 10 with a substantially horizontal line of sight.Hereby the same advantage could be obtained, viz that the camera 10 canbe configured to watch any of the two sides of the piece of cloth.

As shown in FIG. 1 and in the current example, the camera 10 is locatedunderneath the open area between the conveyors 12, 13 and thus thecamera 10 will record an image of that side of the piece of cloth thathas faced towards the ironing side of the rotary ironer 1. This is aconsiderable advantage over previous systems, since the ironing side isthe most smooth, and the side where discolourations, if any, that werenot removed during the preceding laundering procedure are most visible.

In the area 14 between the two conveyors 12,13 there is arranged atransparent cover plate 15 that serves several purposes. It supports thepiece of cloth between the two conveyors, and in this context it hassurprisingly been found that it is possible, without any problemswhatsoever, to push the front end of a piece of cloth transversallyacross the cover plate 15 without folds occurring in the piece of cloth.The cover plate 15 also contributes to making a physical shield for thecamera 10. This is important, since—during passage of the apparatus—thepieces of cloth will emit both a certain amount of heat and some degreeof moisture, which may adversely influence the operational stability ofthe camera 10.

For the same reason the cover plate 15 forms a window in a container 16,in which the camera 10 is located along with the associated mirrorarrangement. Thereby it is possible to maintain a constant climatearound the camera 10. Simultaneously it is ensured that fluff and otherimpurities, which are unavoidable in the surroundings of a laundry, arenot deposited on the mirrors.

FIG. 2 is an enlarged reproduction of the container 16 as such with thecamera 10. The travelling of the light from the underside of a piece ofcloth to the camera is also shown herein. The travelling of the lightfrom the underside of the glass plate 15 via the mirrors S1, S2, S3 andfurther on to the camera 10 is shown by lines L1, L2, L3 and L4.

Glass rods 11 are located each in their holder, and at the end of eachrod, lights sources are provided that are not shown in the figure. Thelight sources are commercially available sources that emit light in adesired spectral area. In the embodiment shown in FIGS. 1 and 2, therods 11 are located to each side of the line L1, and thereby symmetricalillumination of the piece of cloth across the glass plate is obtainedand the advantage of this is that folds, if any, generated during theironing process do not entail shadow formation that could be interpretedas impurities in the piece of cloth. If a sufficiently strong lightsource is used, however, a rod will often be sufficient, which isfinancially advantageous.

This type of light emitters is associated with the problem that thelight intensity has a propensity to decrease with increasing distancefrom the light source, and that the light will have a propensity toleave the rod at a relatively acute angel relative to the longitudinalaxis of the rod. It has been attempted to solve these problems bygrinding a number of discrete facets in the rod surface, whereby theground surface of each facet will serve as diffusion face. Variations inthe distance between the facets enable a more even emission of lightalong the longitudinal axis of the rod, and selection of the anglebetween the surface of the facets and the longitudinal axis of the rodserves to ensure that the light leaves the rod at an angle that israther close to 90°. By these measures it is possible to achieve uniformemission of light along the entire expanse of the rod and at an anglethat does not presuppose a length of the rod that does not considerablyexceed the width of the conveyors.

The area of the glass plate 15 and that of the piece of cloth that is tobe illuminated need not have a width of more than about 2 mm for thesake of the camera. To obtain a high light intensity, it may beadvantageous to position an optical lens between the glass rod 11 andthe plate 15. Hereby the light emitted from the rod can be focused in anarrower area and hence a higher light intensity is accomplished.Likewise, a focusing effect can be obtained by selecting glass rods thatdo not feature circular cross-sections as shown; they rather have across section that comprises two straight parallel sides and twocircular arches that connect each of the two sides. In this contextfacets are ground in the one circular arch and the light will then leaveby the opposite arch.

It is preferred to use a light source that emits light within thespectral range of from 350 nm to 500 nm. Albeit the lower portion ofthis interval is not visible to the camera, the addition of opticalwhitener to the laundry detergents will enable that the light receivedby the pieces of cloth within the lower spectral range will be reflectedwithin the visible area around 450 nm. Hereby a marked improvement isobtained of the contrast between clean and not clean portions of thepiece of cloth, due to the not-clean areas having a propensity to blockthe effect of the contents of optical whitener of the piece of cloth.

In the area above the glass plate 15, a cap 18 is provided that preventslight conditions prevailing in the surrounding environment frominfluencing the illumination of the piece of cloth.

Advantageously the glass plate 15 can be located at a level that isslightly above the level for the receiver and delivery conveyors inorder to thereby ensure that each piece of cloth is caused to slideacross the glass plate. Thereby the glass plate is continuously keptclean which is an essential prerequisite for successful photographing ofthe piece of cloth.

A usual gangway 19 is provided in the area above one of the conveyors.

In a known manner the camera is configured for recording one line at atime in the transverse orientation of the piece of cloth and bycollecting the lines, an overall image is obtained in a conventionalmanner of what passes by on the glass plate 15. In a digital storageunit or a conventional computer 20 this overall image is recorded andanalysed; in the first instance to separate the individual pieces ofcloth from the surroundings, and subsequently to subject the image ofeach piece of cloth to an analysis to detect impurities, spots ordefects in the fabric; and on the basis of the result a signal isemitted to the folding machine 2 to which destination the piece of clothin question is to be sorted to go to.

It will be possible within the framework of the system to also apply abar code to each piece of cloth, which bar code is decoded by theanalysis of the image of the piece of cloth and that identifies eachpiece of cloth. Use of suitable wavelengths of the illumination willalso enable such configuration of a bar code that it is more or lessinvisible to the eye, but readily readable to the camera.

The two conveyors 12 and 13 can be independent units, or they can beintegral parts of the rotary ironer and the folder, respectively.

1. An apparatus for the automatic inspection of flatly positioned piecesof cloth for detecting impurities or other irregularities therein, saidapparatus comprising means for transporting the pieces of cloth past acamera that is, in cooperation with a digital storage unit, configuredfor producing a digital image of each piece of cloth or portions of eachpiece of cloth, one or more light emitters for illuminating at leastthat part of a piece of cloth that is within a field of vision of thecamera, wherein the conveyance transporting means comprises a receiverconveyor and a delivery conveyor, the field of vision of the camerabeing located at least in an open area between these two conveyors and atransparent cover located between the camera and the open area betweenthe two conveyors, whereby a digital image is recorded during thepassage of a piece of cloth from the receiver conveyor to the deliveryconveyor.
 2. The apparatus according to claim 1, wherein the receiverconveyor and the delivery conveyor follow essentially in extension ofeach other and are configured for conveying the piece of cloth slidinglyacross the transparent cover.
 3. The apparatus according to claim 2,wherein the transparent cover forms a window in a closed container inwhich the camera is located.
 4. The apparatus according to claim 3,wherein the one or more light emitters are arranged between the cameraand the transparent cover.
 5. The apparatus according to any one ofclaims 1, 2 or 3, wherein at least one light emitter is an elongatedlight guide that is arranged transversally to the two conveyors in theopen area and wherein the light guide is supplied with light at one orboth ends thereof and emits light along its longitudinal axis.
 6. Theapparatus according to claim 5, wherein each light guide comprises aglass rod that has, along its longitudinal axis, dispersion means forcausing the light to leave the glass rod along its longitudinal axis. 7.A method for the automatic inspection of flatly positioned pieces ofcloth with a view to detecting impurities or other irregularitiestherein, said method comprising the steps of transporting pieces ofcloth past a camera that is, in cooperation with a digital storage unit,configured for producing a digital image of each piece of cloth orportions of each piece of cloth illuminating with one or more lightemitters at least that part of a piece of cloth that is within a fieldof vision of the camera, each piece of cloth being transferred from areceiver conveyor to a delivery conveyor past the field of vision of thecamera located at least in an open area between these two conveyors andover a transparent cover located in the open area between the twoconveyors and between the piece of cloth and the camera and recording adigital image during the passage of a piece of cloth from the receiverconveyor to the delivery conveyor.
 8. The method according to claim 7,wherein the receiver conveyor and the delivery conveyor convey the pieceof cloth slidingly across the transparent cover.
 9. The method accordingto claim 8, wherein the transparent cover forms a window in a closedcontainer in which the camera is located.
 10. The method according toclaim 9, wherein the container is located underneath the two conveyors.11. The method according to claim 7, wherein the receiver conveyorreceives pieces of cloth from a rotary ironer and the delivery conveyordelivers the pieces of cloth to a folding machine that has two or moredestination options for a folded piece of cloth, wherein the relevantdestination is determined by analysis of the recorded digital image ofthe piece of cloth.